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Raumfahrt - Op-ed Lunar Gateway or Moon Direct?

19.04.2019

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An updated illustration of the lunar Gateway, released by NASA March 11, shows the proposed international partner contributions to the facility. On March 26, U.S. Vice President Mike Pence directed NASA to land humans on the moon by 2024, four years earlier than the agency's current plans. Credit: NASA

NASA intends to waste billions on a 'Lunar Orbit Tollbooth.' Private spacecraft could put boots on the moon faster and cheaper.

This op-ed originally appeared in the April 8, 2019 issue of SpaceNews magazine.

NASA has proposed to build a lunar orbiting space station, called the lunar Gateway, to use as a base for lunar exploration. This plan is severely defective.

The Gateway project may be compared to a deal in which you are offered a chance to rent an office in Thule, Greenland, on the following terms: 1. You pay to construct the building. 2. You accept a 30-year lease with high monthly rents and no exit clause. 3. You agree to spend one month per year there for the next 30 years. 4. You agree to fly through Thule whenever you travel anywhere from now on.

Few would find such a proposition attractive. The lunar Gateway project is no better. It will cost a fortune to build, a fortune to maintain, and it will add to the cost, risk, and timing constraints of all subsequent missions to the moon or Mars by adding an unnecessary stop along the way.

To understand just how suboptimal a plan the lunar Gateway is, we need to contrast it with what would be done as part of a well-conceived effort to get the job done as swiftly and as potently as possible. The plan to do lunar exploration this way is called Moon Direct.

Here’s how it would work: In the first phase, which occurs in advance of any human missions, we deliver habitat modules and other cargo one way to the planned base area on the lunar surface.

SpaceX’s Falcon Heavy can lift roughly 60 metric tons to low Earth orbit (LEO). Starting from that point, a hydrogen/ oxygen rocket-propelled cargo lander could deliver 10 tons of payload to the lunar surface.

We therefore proceed by sending two such landers to our planned base location. The best place for it would be at one of the poles, because there are spots at both moon’s poles where sunlight is accessible all the time, as well as permanently shadowed craters nearby where water ice has accumulated. Such ice could be electrolyzed to make hydrogen-oxygen rocket propellant, to fuel both Earth-return vehicles as well as flying rocket vehicles that would provide the base’s crew with exploratory access to most of the rest of the moon. We won’t just be getting a local outpost: we’ll be getting complete global access to an entire world.

The first cargo lander carries a load of equipment, including a solar panel array, high data rate communications gear, a microwave power beaming set up with a range of 100 kilometers, an electrolysis/ refrigeration unit, two crew vehicles, a trailer, and a group of teleoperated robotic rovers. After landing, some of the rovers are used to set up the solar array and communications system, while others are used to scout out the landing area in detail, putting down radio beacons on the precise target locations for the landings to follow.

The second cargo lander brings out a 10-ton habitation module, loaded with food, spare spacesuits, scientific equipment, tools and other supplies. This will serve as the astronauts’ house, laboratory and workshop on the moon. Once it has landed, the rovers hook it up to the power supply and all systems are checked out. This done, the rovers are redeployed to do detailed photography of the base area and its surroundings. All this data is sent back to Earth, to aid mission planners and the science and engineering support teams, and ultimately form the basis of a virtual reality experience that will allow millions of members of the public to participate vicariously in the missions.

The base now being operational it is time to send the first crew. A Falcon Heavy is used to deliver another cargo lander to orbit, whose payload consists of a fully fueled Lunar Excursion Vehicle (LEV). This craft consists of a 2-ton cabin like that used by the Apollo-era Lunar Excursion Module together with an 8-ton hydrogen/oxygen propulsion system, capable of delivering it from the lunar surface to Earth orbit. A human-rated SpaceX Falcon 9 rocket then lifts the crew in a Crew Dragon capsule to LEO where they transfer to the LEV. Then the cargo lander takes the LEV, with the crew aboard, to the moon, while the Crew Dragon remains behind in LEO.

After landing at the moon base, the crew completes any necessary set up operations and begins exploration. A key goal will be to travel to a permanently shadowed crater and, making use of power beamed to them from the base, use telerobots to mine water ice. Hauling this treasure back to the base in their trailer, the astronauts will feed the water into the electrolysis/refrigeration unit, which will transform it into liquid hydrogen and oxygen. These products will then be stored in the empty tanks of the cargo landers for future use — primarily as rocket propellant but also as a power supply for fuel cells and a copious source of life support consumables.

Having spent a couple of months initiating such operations and engaging in additional forms of resource prospecting and scientific exploration, the astronauts will enter the LEV, take off and return directly to Earth orbit. There they will be met by a Crew Dragon — either the one that took them to orbit in the first place or another that has just been launched to lift the crew following them — which will serve as their re-entry capsule for the final leg of the journey back home.

After several such second-phase missions have been completed, a large stockpile of propellant will be in place at the base, and the water acquisition and propellant manufacture operations will have been reduced to practice so that they can be done in a fully automated fashion. We will also have several used LEVs, available, floating in Earth orbit. This being the case, the third phase missions can be done simply by using a medium-lift Falcon 9, (or Blue Origin New Glenn or United Launch Alliance Vulcan) to lift the crew to orbit in a capsule, after which they transfer to a LEV along with 7.5 tons of refueling propellant, and then take flight to the moon. Furthermore, once on the moon, the LEV can be refueled at the base propellant depot for sortie flights to distant locations, before it is ultimately refueled for the return flight home.

With more gear arriving on every mission, the base capabilities will rapidly increase, its supportable population will grow, and mission durations will expand from weeks to months, or even years. As this occurs, the base will transition from a local activity to a center supporting a vigorous globe-spanning program of lunar exploration.

Now let’s compare this plan with one involving the use of the lunar Gateway. The Gateway plan involves using SLS boosters, launchable once every two years, to deliver four modules to build the station in lunar orbit. This will take eight years, which, at an SLS program cost of $2.5 billion per year will stick U.S. taxpayers with a bill for $20 billion, not counting the cost of the station hardware itself, which probably will cost another $10 billion. (In information released March 11, NASA suggested that it would use commercial launchers to build the station. In this case, the space agency will pay $2.5 billion per year for the SLS without using it, plus the cost of the station hardware, plus the cost of the commercial launches.) Then, following this very costly delay, an SLS launch will be used to send a crew to the station in an Orion capsule. There they will need to wait until yet another SLS launch delivers a fully fueled lander to the station, which they will use to sortie to the surface of the moon and back, after which they will ride the Orion home to Earth. So, two SLS launches will be needed at a launch cost per mission of $5 billion — if it is feasible to double the SLS launch rate to one per year. They will also need to do three mission-critical rendezvous maneuvers, including a life-critical rendezvous with the station on their way home. Since the lunar Gateway will be in an 11-day orbit, opportunities to catch the ride back to Earth will occur infrequently. If they miss the bus, they could be out of luck.

Of course, if someone were to also establish a polar moon base with propellant production capability — as proposed in the Moon Direct plan — and develop a LEV to be refueled at the base, it could be used as a reusable ferry between the moon base and the lunar Gateway. This would be a very smart thing to do, as in this case only one SLS launch would need to be used per lunar mission, to deliver the crewed Orion from Earth to the Gateway.

However, since the round-trip propulsion requirement to travel between the Gateway and the lunar surface (a delta-V of 6 km/s) is identical to that needed to fly one-way from the lunar surface to low Earth orbit, the very same LEV that might serve as a ferry between the moon base and the Gateway could also be used to fly from the moon base straight back to LEO. There it could be refitted with a crew and sufficient propellant to send it back to the moon using a single Dragon-carrying Falcon 9 launch, costing just $65 million. Not only would this reduce mission launch costs by a factor of 40, but their mission mode would be far safer, since seen from the surface of the moon, the Earth is always in the same place, so the launch window home is always open. Furthermore, in contrast to the SLS which can only hope to launch once per year, Falcon 9s are already flying twice a month. So not only will we have a moon base, but we will actually be able to use it.

In short, in return for delaying our arrival on the moon by eight years and spending $30 billion to build the Gateway, NASA will enable a lunar base program costing $2.5 billion per flight instead of $65 million per flight, and will be less safe and far less useful than would readily be possible if we had no Gateway at all!

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In Phase 1 of the Moon Direct program, two Falcon Heavy boosters are used to emplace base habitation modules and other cargo on the moon. In Phase 2, one Falcon Heavy and one Falcon 9 are used to deliver the crew to the moon in a fueled Lunar Excursion Vehicle (LEV). In Phase 3, only one Falcon 9 is used to deliver the crew to orbit and refuel the LEV. The crew then flies to the moon in the LEV, which refuels at the lunar base. Credit: Robert Zubrin

Yet the problem with NASA’s planned Lunar Orbit Tollbooth (to use more accurate terminology) is much bigger than the waste of decades of time and tens of billions of dollars and the harmful distortions it would impose on subsequent mission planning. The deeper problem is the form of thinking it represents.

NASA’s astronomy and robotic planetary exploration programs have achieved epic accomplishments because they are purpose-driven. In contrast, since the end of Apollo, NASA’s human spaceflight program has been purpose-free, or to put the matter less charitably, vendor-driven. As a result, its accomplishments have been negligible.

The science programs spend money to do things. The human spaceflight program does things to spend money.

The situation is truly ironic. With the success of Falcon Heavy, America could be poised right now for a breakthrough into space. The cash available is adequate. The Lunar Orbit Tollbooth funds, if spent instead on contracts for entrepreneurial development of Moon Direct landers and excursion vehicles, could enable a return to the moon within four years. With potent lunar exploration missions requiring only a single medium-lift launch each, the moon base will be eminently sustainable, and the nation will be able to direct its heavy-lift capabilities, and with them its ambitions, toward Mars.

Instead of being uselessly confined to a can in lunar orbit, America’s astronauts can be the explorers of new worlds. As we did in the 1960s, we can once again astound the world with what free people can do. With the approach of the 50th anniversary of the first moon landing reminding us of the sort of things we as a nation once accomplished, we should resolve to do no less.

Quelle: SN

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